<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!--
    http://127.0.0.1:8080/detectusername/userServlet

    请求体：username=zhangsan
    -->
    <form method="get" action="userServlet">
        用户名:<input type="text" name="username"><br>
        <input type="submit" value="校验">

    </form>
</body>
</html>